Advancements in the fields of electronics and communications have permitted the introduction and commercialization of many new types of communication systems. Information can be affordably communicated to locations in manners previously not possible or affordable.
The field of cellular telephony is exemplary of a communication system that has been made possible due to such advancements. Communication using a cellular telephone or other radiotelephonic system is advantageous because a fixed, wireline connection is not required between a sending station and receiving station to permit communications to be effectuated therebetween. A cellular or other radiotelephonic communication system is therefore particularly advantageous to effectuate communications when the use of fixed or hard-wired connections would be inconvenient or impractical. Continued advancements in the field of cellular telephony, as well as other types of radiotelephonic communications, have permitted the introduction of new services and new forms of communication pursuant to already-installed cellular, and other radiotelephonic, networks.
Proposals have been set forth to provide existing cellular, and other communication networks, with the capability of communicating packet data. Information to be transmitted between a sending station and a receiving station is formed into discrete packets of data. Individual packets can be sent on a communication channel from the sending station to the receiving station. Because the information is communicated by way of discrete packets, the sending station need utilize the channel only during the time periods required to send the discrete packets. A channel is typically, therefore, a shared channel used by a plurality of sending stations.
To communicate a packet of data to a mobile station, the packet must be addressed with an identification address of the mobile station. An Internet Protocol (IP) address is exemplary of an identification address that can be used to address packets of data that are to be relayed to the mobile station. The IP address is, of course, utilized when transmissions are made pursuant to an Internet Protocol. Many different types of services have been implemented that are effectuated by the communication of packet data according to various other protocols.
The Point-to-Point Protocol (PPP) is a protocol that provides Point-to-Point access and enables networking over serial lines. PPP is the protocol used by the cdma2000 wireless communication standard for communications between, for example, mobile stations and Packet Data Service Nodes (PDSNs). The cdma2000 wireless communication standard is a third generation technology that increases data transmission rates in CDMA (code division multiple access) systems. A packet data transfer session between a mobile station and a PDSN is referred to as a PPP session.
Transmission Control Protocol/internet Protocol (TCP/IP) is the protocol of the Internet and has become the global standard for communications. TCP provides transport functions that insure that the total amount of bytes sent is received correctly. IP provides a routine mechanism. TCP/IP is a routeable protocol, which means that messages contain not only the address of a destination station, but also the address of a destination network. Every user in a TCP/IP network requires an IP address. In Simple IP, which is used by non-mobile Internet users, a new IP address is dynamically assigned every time a user negotiates a PPP session.
Mobile Internet Protocol (Mobile IP) is a protocol designed to support mobile Internet access. Mobile IP permits continuous network connectivity anywhere a mobile station happens to be located. Mobile IP is able to track a mobile station without having to change the mobile station's permanent IP address. Under mobile IP, data is transmitted to a permanent address of the mobile station, which is associated with a home agent of the mobile station. Most typically, when the mobile station is outside its home network, the home agent will forward data to the mobile station in care of a foreign agent through a process of encapsulating the data, most typically referred to as tunneling. Once the data packets are received by the foreign agent, the data will be de-capsulated and forwarded to the mobile station. In contrast to Simple IP, in Mobile IP users may keep their permanent IP address, which can be used each time the user negotiates a PPP session.
Layer Two Tunneling Protocol (L2TP) is a method for encapsulating standard PPP through a variety of media. L2TP also allows encapsulation of PPP using User Data Protocol (UDP) packets. L2TP supports non-IP protocols such as AppleTalk and IPX as well as LPSec Security Protocol. L2TP is implemented to provide secure, node-to-node communications in support of multiple, simultaneous tunnels in an IP-based network. L2TP offers PPP access to users from remote locations. In contrast to Simple IP, an L2TP user may keep a permanent IP address that can be used each time the user negotiates a PPP session.
When L2TP is used in cdma2000, an L2TP Access Concentrator functionality is performed by the PDSN to which the mobile station is connected. An L2TP Network Server is a separate node from the PDSN. In contrast to Mobile IP and Simple IP, under L2TP PPP negotiations are performed in two parts, a first part involving the L2TP Access Concentrator (i.e., the PDSN) and a second part involving the L2TP Network Server.
When a mobile station is engaged in a PPP session, the mobile station will often need to be handed over between different cells of a wireless communication system. Sometimes these handovers of the mobile station require that handling of the PPP session be transferred from a first PDSN to a second PDSN. Such inter-PDSN handovers typically occur when, following the handover, the radio network serving the mobile station cannot connect to the first PDSN such as, for example, when the radio network is not aware of the first PDSN, when the radio network belongs to an operator that does not wish to use the first PDSN, or when the network topology does not allow the radio network to reach the first PDSN.
In connection with an inter-PDSN handover, a PPP session begun prior to the handover must be completely renegotiated, even though most often the session parameters from the PPP session initiated with the first PDSN could be reused. These parameters (commonly referred to as a PPP context) could be reused because the session on the second PDSN will very frequently have the same characteristics as when the mobile station was being served by the first PDSN. The PPP includes several sub-protocols, each of which can include parameters such as, for example, compression, encryption, or character escaping. Once PPP negotiation of a PPP session has been completed, packet data payload can be transferred. The PPP context comprises negotiated values of the PPP parameters. Particular parameters included in the PPP context can differ from one implementation to another. The PPP context could consist, for example, of a table containing the following information: User identification (e.g., International Mobile Station Identifier), Sub-protocol Identifier (e.g., Link Control Protocol, Compression Control Protocol), Option (e.g., Escaped characters, Compression Protocol Identifier), Value (e.g., Escape only character X, use Y compression scheme). Of course, reuse of the parameters is not useful when Simple IP, rather than Mobile IP or L2TP is used, since in Simple IP a new IP address is assigned every time a user negotiates a PPP session.
Renegotiation of a PPP session of a mobile station as a result of an inter-PDSN handover is therefore often unnecessary and constitutes a significant waste of time and system resources. An interruption in packet data services to a mobile station due to the need to renegotiate such a session can take up to ten seconds. Such a delay may be long enough to cause failures in real-time applications that are running on the mobile station. There is accordingly a need for a method and system for transfer of a mobile station's PPP context when the mobile station undergoes an inter-PDSN handover.